Determine either True or False or each question and explain the reason.

a. Applicant developers prefer to use API rather than directly invoking system calls.

b. Generally, while UNIX/Linux system calls are short and less descriptive, the system calls in Windows are longer and more descriptive.

c. Applications compiled on one operating system can be executed directly on another operating system if they have similar OS structures.

d. Separation of policy from mechanism is an essential principle of operating system design.

e. Mac OS X is a hybrid system consisting of both the Mach microkernel and BSD UNIX.

f. iOS and Android combine different structures, resulting in hybrid systems that address performance, security, and usability issues.